Genome-wide Analysis Of Gras Gene Family In Citrus Sinensis

GRAS genes are putative plant-specific transcriptional factors which participate in plant growth and development.GRAS proteins are named after first three functionally identified members in this family:GAI,RGA and SCR.Generally,GRAS proteins are constituted by a variable N-terminal and a conserved C-terminal.Researches of GRAS family in a lot of species have been completed,but genome-wide overview of the GRAS gene family in citrus has not been available.Sweet orange is the most important fruit tree in citrus.With the release of whole genome sequencing data,it provides resources and evidences to the research of GRAS family in citrus.In this work,50 putative CsGRAS genes in Citrus sinensis were identified from two whole genome sequencing database of sweet orange.Distribution mapping showed that CsGRAS genes were nonrandomly localized in 9 chromosomes.Tandem repeats and segmental repeats were showing in the map.All GRAS proteins were classified into eleven subfamilies according to the phylogenetic tree among Citrus sinensis,Arabidopsis and rice.In particular,the CsGRAS34 subfamily was specific to sweet orange.Part of CsGRAS protein,which had been functionally predicted by phylogenetic analysis,were confirmed by PPI network.Six species,including Citrus sinensis were compared to indicate that the subfamilies among species were conservative.AtSCR subfamily and AtPATl subfamily were revealed to be the most conservative subfamilies among these species.In addition,the expression patterns of GRAS genes exhibit differences in four tissues based on RNA-seq data and RT-PCR analyses.Phosphorous is one of the most important nutrient element in plant growth and development.Although,a large scale of genes and methylation modification have been identified in response to phosphorous deficiency,but there are little researches in GRAS family.Furthermore,we experimentally investigated the expression profiles of 40 GRAS genes in the root of Poncirus(a close relative of citrus)in response to phosphate deficiency treatments.Several candidate CsGRAS genes that might play an important role in responding to phosphate deficiency in orange.GRAS proteins compared of less than or nearly 200 amino acid residues,which are called small GRAS proteins,seem to widely exist among all terrestrial plants.The expression levels of their genes were extremely low.Taken together,this comprehensive analysis will provide a variable for studies of GRAS gene family in Citrus.